Scope: Prion diseases are infectious diseases affecting humans and animals. They are caused by mis-folding of a normal cellular protein (the prion protein, PrP) into infectious forms (prions), which then propagate themselves by templating more mis-folding events. Reactive oxygen/nitrogen species (ROS/RNS) are formed as byproducts of many cellular processes and can be used as signalling intermediates within the cell. Oxidative stress occurs when the balance between production and detoxification is tipped in favour of increased reactive species, resulting in damage to the cellular components. Our research aims to investigate the relationships between PrP, prions and prion disease with ROS and ROS-producing systems, such as cell metabolism and signal transduction, to generate a significant understanding of both PrP function and prion disease pathogenesis. Research materials, equipment and methods: Our research predominantly uses cell-based techniques to investigate changes in single cells or in cell networks. We have generated a number of cell models, including mouse and human stem cell models. To investigate specific redox-related pathways we use a combination of protein, RNA, live cell function and microscopy analyses. Research accomplishments: Using stem cell models permits the generation of cultures of brain cells that represent a more complete model of brain tissue by generating highly organized regions of tissue containing neurons, astrocytes and oligodendrocytes. We have developed the human stem cell system to produce the first human brain tissue model of prion disease. This was achieved by infecting cerebral organoid (mini-brain) culture system with prions. We further demonstrated that cerebral organoid prion infections can reproduce certain features of prion disease that are found in human brains post-mortem. The organoids showed changes in health parameters, metabolism and cytokine release, and production of disease-associated prions in a manner that was influenced by the infecting prion inoculum and by the underlying cells within the organoid.